Process for the recovery of organic acids

ABSTRACT

The present invention relates to a process for the recovery of an organic acid from a fermentation broth which comprises drying the fermentation broth to obtain a dried product, adding the dried product to a lower alcohol in the presence of an acid, and then removing the insoluble material to obtain an organic acid. In accordance with the recovery process of the present invention, organic acids of a high purity can be recovered in high yields from the whole fermentation solution containing various impurities with fewer steps as compared with conventional methods.

CROSS REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of the filing date of U.S.Provisional Application No. 60/147,031, filed Aug. 3, 1999, which isherein incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to a process for the recovery andpurification of organic acids from an aqueous solution, such as afermentation broth.

[0004] 2. Related Art

[0005] Organic acids are important chemicals of commerce, having manyuses in the food and pharmaceutical industries. Lactic acid, forexample, can be added to a variety of food stuffs as a preservative andis used in medical preparations and as a monomer in the manufacture ofbiodegradable plastics used in sutures, prosthetics and controlledrelease drug delivery systems.

[0006] Organic acids can be produced either by chemical synthesis or bymicrobial fermentation. Historically, organic acids were produced fromanimal fat or vegetable oil sources or from petroleum sources insubstantially non-aqueous systems. However, since a number ofmicroorganisms are known to produce valuable organic acids, methods havebeen developed for the recovery of organic acids produced by microbialfermentation. See, e.g., U.S. Pat. Nos. 5,681,728; 5,034,105; 5,002,881;and 4,882,277.

[0007] In the process for preparing organic acids, the step offermentation is relatively simple. However, the steps of recovery andpurification of the product, i.e. an organic acid, are usuallycomplicated with poor efficiency. For example, recovery of arepresentative organic acid, 2-keto-L-gulonic acid, is made as follows.

[0008] 2-keto-L-gulonic acid is a significant intermediate in thepreparation of L-ascorbic acid (vitamin C), an essential nutrient. Inthe past, 2-keto-L-gulonic acid has been synthesized on an industrialscale using the Reichstein method (Helvetica Chimica Acta 17:311(1934)). This method, however, has a number of disadvantages forcommercial application, including the use of large quantities ofsolvents and the involvement of a number of complex reaction steps.

[0009] Accordingly, as an alternative to the Reichstein method, a numberof processes employing one or more microorganisms have been developedfor the commercial production of 2-keto-L-gulonic acid by fermentation.U.S. Pat. No. 2,421,611, for example, discloses a method involvingmicrobial oxidation of D-glucose to 5-keto-D-gluconic acid, followed bychemical or microbial reduction to L-idonic acid and subsequentmicrobial oxidation to 2-keto-L-gulonic acid. Fermentative pathwaysinvolving oxidation of L-sorbose to 2-keto-L-gulonic acid via asorbosone intermediate have also been developed using, for example,Gluconobacter oxydans (U.S. Pat. Nos. 4,935,359; 4,960,695; and5,312,741), Pseudogluconobacter saccharoketogenes (U.S. Pat. No.4,877,735), Pseudomonas sorbosoxidans (U.S. Pat. Nos. 4,892,823 and4,933,289), and mixtures of microorganisms (U.S. Pat. Nos. 3,234,105;3,907,639; and 3,912,592).

[0010] Similar to fermentation processes utilized for the manufacture ofother organic acids, the 2-keto-L-gulonic acid which results as ametabolic product is usually neutralized by the addition of a base, e.g,sodium hydroxide or calcium hydroxide, in order to control the pH valueand maintain favorable fermentation conditions. The product of thefermentation is an aqueous, biomass-containing fermentation solution inwhich the 2-keto-L-gulonic acid salt, e.g., the sodium, potassium,ammonium or calcium salt, is present in dissolved form. However, thefree organic acids and their derivatives are the articles of commercialinterest.

[0011] For example, in the industrial manufacture of L-ascorbic acid,the fermentatively produced 2-keto-L-gulonic acid must be transferredinto an organic solvent, such as a lower alcohol. The salt form of2-keto-L-gulonic acid, however, is practically insoluble in organicsolvents. Therefore, for producing L-ascorbic acid with an industrialadvantage, it is most preferable to employ the synthetic intermediate2-keto-L-gulonic acid as a free acid.

[0012] Prior to conversion into ascorbic acid, however, 2-keto-L-gulonicacid must first be isolated from the fermentation broth. As described inU.S. Pat. No. 4,990,441, for example, 2-keto-L-gulonic acid can berecovered from a fermentation broth by a process comprising the stepsof: (a) removing insoluble material from the broth by centrifugation inthe presence of a flocculating agent, filtration in the presence of aflocculating agent and a filtration additive, or ultrafiltration; (b)removing inorganic cations by acidification; and (c) isolating2-keto-L-gulonic acid by crystallization and drying. High yields of2-keto-L-gulonic acid are difficult to obtain by this method, however,due to the number of steps required and the high solubility of2-keto-L-gulonic acid in the crystallization mother liquor.

[0013] U.S. Pat. No. 5,852,211 describes a process for the conversion ofthe sodium salt of 2-keto-L-gulonic acid, which is present in an aqueousfermentation solution, into an alcoholic solution of the free acid. Thedisclosed process comprises the steps of: (a) crystallizing sodium2-keto-L-gulonate monohydrate from an aqueous fermentation solution; (b)separating the sodium 2-keto-L-gulonate monohydrate crystals from theaqueous fermentation solution; (c) suspending the sodium2-keto-L-gulonate monohydrate in a lower alcohol with acid at a pH in arange from about 1.5 to about 3.5 whereby the acid is converted to theinsoluble sodium salt of the acid and the sodium 2-keto-L-gulonatemonohydrate is converted to free 2-keto-L-gulonic acid; and (d) removingthe sodium salt of the acid to obtain an alcoholic solution of2-keto-L-gulonic acid. Due to the number of steps and the highsolubility of the sodium 2-keto-L-gulonic acid that remains in thecrystallization mother liquor, however, high yields of 2-keto-L-gulonicacid are likewise difficult to achieve.

[0014] Known methods for the recovery and purification of other organicacids produced by fermentation, such as lactic or succinic acid, alsocontain numerous steps and/or produce less than optimal yields. See,e.g., U.S. Pat. Nos. 5,681,728; 5,522,995; 5,503,750; and 5,034,105.Accordingly, there remains a need for a simplified process for theconcentration, recovery and purification of organic acids from aqueoussolutions, such as fermentation broths, in high yields.

SUMMARY OF THE INVENTION

[0015] It is therefore an object of the present invention to provide asimplified process for the recovery and purification of organic acids inhigh yields from a fermentation broth. Other objects, features andadvantages of the present invention will be set forth in the detaileddescription of preferred embodiments that follows, and in part will beapparent from the description or can be learned by practice of theinvention. These objects and advantages of the invention will berealized and attained by the methods particularly pointed out in thewritten description and claims hereof.

[0016] These and other objects are accomplished by the methods of thepresent invention, which, in a first embodiment, are broadly directed toa process for the recovery of an organic acid from a fermentation brothwhich comprises drying the fermentation broth to obtain a dried product,adding the dried fermentation product to a lower alcohol in the presenceof an acid, and then removing the insoluble material to obtain theorganic acid. Other preferred embodiments of the present invention willbe described in more detail below.

[0017] It is to be understood that both the foregoing generaldescription and the following detailed description are exemplary andexplanatory only and are intended to provide further explanation of theinvention as claimed.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] In one aspect of the invention there is provided a process forthe recovery of an organic acid from a fermentation broth whichcomprises:

[0019] (a) drying the fermentation broth to obtain a dried product;

[0020] (b) adding the dried product to a lower alcohol in the presenceof an acid; and

[0021] (c) removing the insolubles to obtain an organic acid.

[0022] As used herein, the term “organic acid” or grammaticalequivalents means a substituted or unsubstituted alkyl group containingone or more carboxyl groups, —COOH, i.e. a carboxyl acid. The organicacids can be obtained from a fermentation conversion of saccharides suchas starch, sucrose or glucose or from n-paraffins.

[0023] A non-exclusive list of examples of organic acids which can berecovered using the inventive process includes lactic acid,2-keto-L-gulonic acid, tartaric acid, citric acid, acetic acid, maleicacid, malic acid, malonic acid, succinic acid, salicylic acid, glycolicacid, glutaric acid, gluconic acid, benzoic acid, formic acid, propionicacid, pivalic acid, oxalic acid, toluic acid, stearic acid, ascorbicacid, pamoic acid, glutamic acid, fumaric acid or mixtures thereof. In apreferred embodiment, the recovered organic acid is lactic acid,2-keto-L-gulonic acid, citric acid or gluconic acid.

[0024] It has been surprisingly and advantageously found that organicacids of a high purity can be recovered at high yields using the wholedried fermentation broth as the starting material. With the aid of theprocess in accordance with the invention, organic acids such as lacticacid and 2-keto-L-gulonic acid, which usually occur as a dissolved saltin the aqueous fermentation solution, can be recovered in a relativelysimple and economical manner into an alcoholic solution of the freeacid.

[0025] Following recovery of the organic acids according to the presentinvention, the organic acids can be further treated, if necessary, inorder to render them suitable for their intended purpose. For example,the thus-obtained solution of 2-keto-L-gulonic acid can subsequently beconverted into ascorbic acid in any known manner. See, e.g., U.S. Pat.No. 5,391,770.

[0026] Any fermentation broth containing the desired organic acid(s), aprecursor thereof or its water-soluble salt can be used in the presentinvention. Such a fermentation broth, which is effected prior to theactual process in accordance with the invention, can be obtained by anyconventional means, such as microbial fermentation. See, e.g., U.S. Pat.Nos. 5,834,231 and 5,705,373. Further, the microbes used in thefermentation process may be Protists (yeast or fungi) or bacteria, andthe fermentation itself may be either aerobic or anaerobic.

[0027] The fermentation broth used in the present invention istypically, but not always, a fermentation broth produced by thecultivation of one or more microorganisms that produce a specificorganic acid(s) and/or a precursor thereof. Any microorganism(s) whichproduces the desired organic acid can be used to prepare thefermentation broth. The organic acid producing microorganisms which canbe used, for example, include bacteria belonging to the generaLactobacillus, Pseudogluconobacter, Pseudomonas, CorynebacteriumAcetobacter, Gluconobacter, Aspergillus, Brevibacterium and bacteriabelonging to the genus Erwinia. See, e.g., Atkinson and Mavituna,Biological Engineering and Biotechnology Handbook 421 (1983).

[0028] A temperature suitable for each species of microorganism used isemployed as the fermentation temperature. It is usually from about 25°C. to about 60° C. In addition, most of the organic acid-producingmicroorganisms have an acid sensitivity which require the medium to havea pH from about 3 to about 9.

[0029] The composition of the fermentation medium where an organic acidis produced using the above-mentioned microorganisms can be any onewhich is suitable for an organic acid producing microorganism to beused. In addition to water and an insoluble biomass, these fermentationbroths generally contain the nutrients required by the microorganism(s)being employed to produce the organic acid. These nutrients include, butare not limited to, amino acids, inorganic and/or organic salts,carbohydrates, and various vitamins and growth factors.

[0030] In one preferred embodiment of the invention, at least part ofthe insolubles are first removed from the fermentation broth prior tothe drying step of the inventive process. The insolubles, e.g.,microorganisms which form the biomass and salts, are preferably removedat the end of fermentation and can be removed by any known mechanicalseparation technique. Such techniques include, but are not limited to,filtration, e.g., ultrafiltration and microfiltration, and separation,e.g., centrifugation and decanting, by which, on the whole, onlyundissolved and/or relatively high molecular weight substances areremoved. In a preferred embodiment, at least part of the insolubles areremoved from the fermentation broth by filtration prior to the dryingstep. Most preferably, at least part of the insolubles are removed byultrafiltration.

[0031] In another preferred embodiment, at least about 90% of theinsolubles are first removed from the fermentation broth prior to thedrying step. The fermentation broth from which some or all of theinsolubles have been removed can then be concentrated prior to drying.In one embodiment, the process for concentrating the fermentation brothis by evaporation.

[0032] Therefore, in one embodiment of the invention, the wholefermentation broth can be used as the starting material for the recoveryof the organic acid. In another embodiment, some or all of the insolublematerial can be removed from the fermentation broth prior to the dryingstep of the inventive process. It is understood that a complete orpartial removal of the insolubles prior to the drying is not necessaryfor the purpose of carrying out the inventive process.

[0033] In the inventive process, the fermentation broth is dried toobtain a dried product. The fermentation broth can be dried by any knownprocess, e.g., by means of a spray dryer, a spin flash dryer or afluidized bed dryer. In a preferred embodiment, the fermentation brothis dried by the use of a spray dryer. In another preferred embodiment,the moisture percentage of the dried product is from about 0.1% to about20% moisture, more preferably from about 0.1% to about 10%. The driedproduct which is obtained contains, among other substances, the desiredorganic acid and all or part or none of the biomass. It was surprisingand particularly advantageous that the fermentation broth could bedried, e.g., spray dried, to obtain an easily handled free flowingpowder.

[0034] According to the inventive process, the dried fermentation brothcontaining, inter alia, the desired organic acid, a precursor thereof orits salt, is added to a lower alcohol in the presence of an acid. In apreferred embodiment, the concentration of the organic acid added to thelower alcohol is from about 50 g/L to about 100 g/L. The lower alcoholemployed in the inventive process can be any lower alcohol which allowsfor the selective recovery of the desired organic acid. Suitable loweralcohols can be determined empirically by those skilled in the art andinclude, e.g., methanol, ethanol, propanol, butanol and glycol. In apreferred embodiment, the lower alcohol is methanol or ethanol, morepreferably anhydrous methanol or ethanol.

[0035] In general, the amount of lower alcohol and acid employed in theinventive process can be any amount which allows for the selectiverecovery of the desired organic acid. In addition, the amount of acidadded will be proportional to the amount of dried product. In apreferred embodiment, the acid is added in stoichiometric proportions orin excess, preferably about 1.2 equivalents of acid is added.

[0036] The acid can be any acid which allows for the selective recoveryof the desired organic acid. For example, a strong acid of low watercontent can be used in the inventive process. The water content of theacid is not critical for the process. However, the concentration ofwater in the resulting organic acid/alcohol solution determines theequilibrium conversion of a subsequent esterification. Therefore, froman industrial-economical point of view, acids of low water content,i.e., acids more appropriately denoted as “concentrated,” are preferablyused. In a preferred embodiment, the water content of the acid is about15% or less. Examples of such acids are sulphuric acid, nitric acid,hydrochloric acid, hydrobromic acid and phosphoric acid, and evengaseous hydrogen chloride. In a preferred embodiment, concentratedsulphuric acid or hydrochloric acid is used. More preferably,concentrated sulfuric acid is used.

[0037] In one embodiment of the invention, the dried fermentationproduct can first be suspended in the lower alcohol prior to theaddition of the acid. The desired organic acid can also be obtained inanother embodiment of the invention whereby the dried product is addedtogether with the acid to a lower alcohol. It is therefore understoodthat both the simultaneous and subsequent addition of acid are includedwithin the scope of the inventive process, although the subsequentaddition of acid is preferred.

[0038] Preferably, the temperature at which the dehydration and acidreactions are carried out lies in the range from about 25° C. to about60° C. In addition, the resulting organic acid should be soluble in thereaction mixture.

[0039] In another embodiment of the invention, there is provided aprocess for the recovery of an organic acid ester from a fermentationbroth. Carboxylic acids react with alcohols in the presence of a strongacid, such as sulfuric acid, to produce esters. Under certain conditionsthe obtained free organic acid of the present invention, together with alower alcohol in the presence of an acid, can be converted into itscorresponding organic acid lower alkyl ester. Accordingly, it isunderstood that the recovered free organic acid as well as thecorresponding organic acid ester are included within the scope of theinventive process.

[0040] According to the inventive process, the insolubles aresubsequently removed from the solution to obtain the desired organicacid. After the dried product is added to a lower alcohol in thepresence of an acid, insoluble salts, e.g., Na₂SO₄, CaSO₄, K₂SO₄,(NH₄)₂SO₄, can be removed readily from the reaction mixture. The removalof the insoluble salts, as well as other insoluble substances, e.g.,residues of biomass or proteins, can be carried out by any knownprocess, such as filtration and/or centrifugation. In a preferredembodiment, the insolubles are removed by filtration. The resultingalcoholic filtrate containing the desired organic acid has a very highpurity.

[0041] Therefore, in accordance with the recovery process of the presentinvention, organic acids of a high purity, i.e., greater than about 80%,can be recovered in high yields, i.e., greater than about 90%,preferably 95% to 99%, from the whole fermentation solution containingvarious impurities with fewer steps as compared with conventionalmethods. The disadvantages of prior art processes, such as the completeremoval of biomass and proteins, the use of cation exchangers to removemetal ions from the aqueous fermentation solutions as well as thecrystallization of the organic acid, are thereby avoided.

[0042] All patents and publications cited in this disclosure areindicative of the level of skill of those skilled in the art to whichthis invention pertains and are all herein incorporated by reference intheir entirety.

[0043] Having now generally described the invention, the same will bemore readily understood through reference to the following Exampleswhich are provided by way of illustration, and are not intended to belimiting of the present invention, unless specified.

EXAMPLE 1

[0044] A fermentation broth was prepared as described in U.S. Pat. No.5,834,231 containing 84 g/L 2-keto-L-gulonic acid, 4 g/L sorbose and 136g/L total dry solids and spray-dried on a high pressure nozzle sprayer(APV Americas; Tonawanda, N.Y.). The feed was preheated to 170° F., anddried with a 495° F. inlet and a 198° F. outlet temperature. A total of8 gallons of feed was dried to give 10.2 lbs. of dried product at 8%moisture.

[0045] 25 g of the spray dried product was slurried into 250 ml ofanhydrous methanol. 3.2 ml of sulfuric acid was added to the solutionover 20 minutes while stirring. The slurry was stirred for an additional60 minutes, filtered and the solids washed with 150 ml of additionalmethanol. The product filtrate of 320 ml contained 35 g/L2-keto-L-gulonic acid and 1.7 g/L of 2-keto-L-gulonic acid methyl ester.The cake of 12 grams contained 3.8% 2-keto-L-gulonic acid and 0.4%2-keto-L-gulonic acid methyl ester, for a yield of 96%.

EXAMPLE 2

[0046] A fermentation broth made similar to that in Example 1 was firstultrafiltered using a 100,000 molecular weight cutoff membrane to removecell solids, and then evaporated to a 1.2 g/ml density before spraydrying. The feed was preheated to 165° F., and dried with a 495° F.inlet and 200° F. outlet temperature. Feed dry solids was 39.2 wt %. Atotal of 10 gallons of feed was dried, to give 42 lbs. of dry product at15% moisture.

[0047] 36 g of the spray dried product was slurried into 250 ml ofanhydrous methanol. 4.2 ml of concentrated sulfuric acid was added over20 minutes. The slurry was stirred for an additional 60 minutes,filtered, and washed with 150 ml of methanol. The product filtrate of335 ml contained 67 g/L 2-keto-L-gulonic acid and 1 g/L 2-keto-L-gulonicacid methyl ester. The cake of 31 g contained 3.0% 2-keto-L-gulonic acidwith no methyl ester, for a yield of 96%.

EXAMPLE 3

[0048] 10 ml of product filtrate obtained by the procedure of Example 2,but containing 71.9 g/L of 2-keto-L-gulonic acid, was placed in a testtube. To this solution was added 0.14 ml of concentrated sulfuric acid.The test tube was placed in an oven at 60° C. for 1 hour to give 1.5g/Lof 2-keto-L-gulonic acid and 77.1 g/L of methyl ester.

EXAMPLE 4

[0049] A fermentation broth of calcium lactate, made from thefermentation of Lactobacillus casei on dextrose, was ultrafiltered andspray dried, using the procedures of Examples 1 and 2, to obtain a dryproduct containing 70.3 wt % lactic acid. 25 g of the spray driedcalcium lactate was slurried into 500 ml anhydrous ethanol. 6.4 ml ofconcentrated sulfuric acid was added over 30 minutes. The slurry wasstirred for an additional 60 minutes, filtered, and washed two timeswith 100 ml ethanol. The filtrate of 490 ml contained 59.1 g/L lacticacid and the wash of 195 ml contained 20.1 g/L lactic acid. The cake of25 g contained 1.8 g/kg lactic acid for a yield of 99%.

EXAMPLE 5

[0050] 17.5 g of the spray dried calcium lactate was slurried into 125ml of anhydrous ethanol. 4.9 ml of concentrated sulfuric acid was addedover 30 minutes. The slurry was allowed to heat to 75° C. with stirringfor one hour. The slurry was filtered and washed two times with 100 mlof ethanol. The filtrate of 200 ml contained 67.9 g/L ethyl lactate and1.6 g/L lactic acid for a total yield of 86.6%.

[0051] In view of the foregoing description taken with the Examples,those skilled in the art will be able to practice the invention invarious enablements and embodiments without departing from the spiritand scope of the invention as defined in the appended claims.

What is claimed is:
 1. A process for the recovery of an organic acidfrom a fermentation broth comprising: (a) drying said fermentation brothto obtain a dried product; (b) adding said dried product (a) to a loweralcohol in the presence of an acid; and (c) removing insolubles toobtain an organic acid.
 2. The process of claim 1, further comprisingremoving the insolubles in said fermentation broth prior to the dryingof step (a).
 3. The process of claim 2, wherein said insolubles areremoved by filtration.
 4. The process of claim 3, wherein saidinsolubles are removed by ultrafiltration.
 5. The process of claim 1,wherein at step (b) the concentration of said organic acid added to saidlower alcohol is from about 50 g/L to about 100 g/L.
 6. The process ofclaim 1, wherein at step (a) the process for drying comprises spraydrying said fermentation broth.
 7. The process of claim 1, wherein thereaction temperature at step (b) is from about 25° C. to about 60° C. 8.The process of claim 1, wherein at step (b) said dried product is addedto a lower alcohol prior to the addition of said acid.
 9. The process ofclaim 1, wherein at step (b) about 1.2 equivalents of acid is added. 10.The process of claim 1, wherein at step (b) said lower alcohol isselected from the group consisting of methanol, ethanol, propanol,butanol and glycol.
 11. The process of claim 1, wherein at step (b) saidacid is selected from the group consisting of sulphuric acid, nitricacid, hydrobromic acid, hydrochloric acid and phosphoric acid.
 12. Theprocess of claim 11, wherein at step (b) said acid is sulphuric acid.13. The process of claim 1, wherein at step (c) the process for removinginsolubles comprises filtration.
 14. The process of claim 1, whereinsaid organic acid comprises lactic acid, 2-keto-L-gulonic acid, citricacid or gluconic acid.
 15. The process of claim 14, wherein said organicacid is 2-keto-L-gulonic acid.
 16. The process of claim 1, furthercomprising esterifying said organic acid (c) to the corresponding ester.17. A process for the recovery of an organic acid from a fermentationbroth comprising: (a) drying said fermentation broth to obtain a driedproduct; (b) adding said dried product (a) to a lower alcohol to obtainan alcoholic suspension; (c) adding an acid to said alcoholic suspension(b); and (d) removing the insolubles to obtain an organic acid.
 18. Theprocess of claim 17, further comprising removing the insolubles in saidfermentation broth prior to the drying of step (a).
 19. The process ofclaim 18, wherein said insolubles are removed by filtration.
 20. Theprocess of claim 19, wherein said insolubles are removed byultrafiltration.
 21. The process of claim 17, wherein at step (b) theconcentration of said organic acid added to said lower alcohol is fromabout 50 g/L to about 100 g/L.
 22. The process of claim 17, wherein atstep (a) the process for drying comprises spray drying said fermentationbroth.
 23. The process of claim 17, wherein the reaction temperature atsteps (b) and (c) is from about 25° C. to about 600° C.
 24. The processof claim 17, wherein at step (b) said lower alcohol is selected from thegroup consisting of methanol, ethanol, propanol, butanol and glycol. 25.The process of claim 17, wherein at step (c) about 1.2 equivalents ofacid is added.
 26. The process of claim 17, wherein at step (c) saidacid is selected from the group consisting of sulphuric acid, nitricacid, hydrobromic acid, hydrochloric acid and phosphoric acid.
 27. Theprocess of claim 26, wherein at step (c) said acid is sulphuric acid.28. The process of claim 17, wherein at step (d) the process forremoving insolubles comprises filtration.
 29. The process of claim 17,wherein said organic acid comprises lactic acid, 2-keto-L-gulonic acid,citric acid or gluconic acid.
 30. The process of claim 29, wherein saidorganic acid is 2-keto-L-gulonic acid.
 31. The process of claim 17,further comprising esterifying said organic acid (d) to thecorresponding ester.
 32. A process for the recovery of an organic acidester from a fermentation broth comprising: (a) drying said fermentationbroth to obtain a dried product; (b) adding said dried product (a) to alower alcohol in the presence of an acid; (c) esterifying the freeorganic acid to the corresponding ester; and (d) removing insolubles toobtain an organic acid ester.
 33. The process of claim 32, furthercomprising removing the insolubles in said fermentation broth prior tothe drying of step (a).
 34. The process of claim 33, wherein saidinsolubles are removed by filtration.
 35. The process of claim 34,wherein said insolubles are removed by ultrafiltration.
 36. The processof claim 32, wherein at step (b) the concentration of said organic acidadded to said lower alcohol is from about 50 g/L to about 100 g/L. 37.The process of claim 32, wherein at step (a) the process for dryingcomprises spray drying said fermentation broth.
 38. The process of claim32, wherein the reaction temperature at steps (b) and (c) is from about25° C. to about 60° C.
 39. The process of claim 32, wherein at step (b)said lower alcohol is selected from the group consisting of methanol,ethanol, propanol, butanol and glycol.
 40. The process of claim 32,wherein at step (b) about 1.2 equivalents of acid is added.
 41. Theprocess of claim 32, wherein at step (b) said acid is selected from thegroup consisting of sulphuric acid, nitric acid, hydrobromic acid,hydrochloric acid and phosphoric acid.
 42. The process of claim 41,wherein at step (b) said acid is sulphuric acid.
 43. The process ofclaim 32, wherein at step (d) the process for removing insolublescomprises filtration.
 44. The process of claim 32, wherein said organicacid comprises lactic acid, 2-keto-L-gulonic acid, citric acid orgluconic acid.
 45. The process of claim 44, wherein said organic acid is2-keto-L-gulonic acid.